Need help with a mark iv problem.

[Bshizzle]

So my Mark IV keeps blowing fuses.
It starts humming real loudly, then it just dies when the fuse blows.
I've changed the fuse a few times and the amount of time it goes before it blows varies.

Any ideas?

 

[Mark Fore]

Have you changed your power tubes recently and maybe put the wrong ones in?

 

[acorkos]

put it in class A operation and remove the inner 2 x power tubes. if it still hums, then your outer tubes are probably bad. if it doesn't hum, then your inner tubes are probably the bad guys. replace the appropriate pair.

 

[Bshizzle]

It doesn't hum all the time.
I replace the fuse, turn it on, and it works like normal.
It starts to hum real loudly right before the fuse blows. It's only for a few seconds.

The first time I replaced the fuse, the amp worked all night and part of the next band practice.

Do you guys think it could just be tubes?
I retubed the whole thing about 6-8 months ago.

 

[bryan_kilco]

It doesn't hum all the time.
I replace the fuse, turn it on, and it works like normal.
It starts to hum real loudly right before the fuse blows. It's only for a few seconds.

The first time I replaced the fuse, the amp worked all night and part of the next band practice.

Do you guys think it could just be tubes?
I retubed the whole thing about 6-8 months ago.

hmmm...I do believe the lifespan of power tubes is about 1-2 years?

I have a set of GT's in my 5150 and last practice they started making a bit of noise when I set something on top of the head. Then, I thought about it, and realized those tubes were about a year and 3 months old.....

 

[Bshizzle]

Well, reading through the manual, it says that a blown fuse is almost always causes by bad power tubes. I guess I'm gonna replace them.

 

[acorkos]

i've seen new production power tubes die right out of the box, so anything is possible.

 

[angelo]

Sometimes lightbulbs just burn out ........

Guess the power tubes first. Even if they work intermittently.

Follow the tube instructions as posted before, or just do what I would do --- get 4 new ones.

 

[angelo]

Just to add, to me it's a no brainer to go the new tube route. I'd hate to be playing a gig and have issues like that. Sorry, just had to add on

 

[Bshizzle]

Thanks guys, I'm gonna get some new power tubes as soon as I get the 80 bones or so for them.